The present invention relates to the controlled release of compounds utilizing a plastic dispenser with a porosigen contained therein.
More specifically, the invention relates to the controlled release of organotins and other compounds utilized as a molluscicide, the controlled release of, larvicides, as well as the controlled release of trace nutrients, nematicides, soil insecticides, etc., from a plastic dispenser.
It is well known that biocidal materials can be incorporated into an elastomer matrix and caused to release at a rate efficacious with pest destruction. U.S. Pat. No. 3,417,181 teaches that organotin toxicants can be dissolved in an elastomer-type matrix and caused to release through a diffusion-dissolution mechanism when exposed to water. The crux of this semial invention was keyed to the necessity of the agent being soluble in the polymer. Similarly, U.S. Pat. Nos. 3,590,119; 3,426,473; 3,851,053; and 3,639,583 extend the scope of the art to embrace new formulations encompassing different elastomers, specific release regulants that affect the diffusion path length, and the like, but again the key concept is the necessity of agent solubility in the elastomer. Agents incorporated are organic pesticides, and the generic matrix type is elastomers such as natural rubber, styrene-butastyrene rubber, and the like. In contrast, U.S. Pat. No. 4,012,221 teaches that inorganic copper salts capable of being released into water are incorporated in a moderately crosslinked elastomer in which the copper salts are insoluble.
It is well known to the compounding art that agents not soluble within a polymeric matrix wil not move at an efficacious rate through said matrix to said matrix surface and thus enter the ambient environment.
Almost all organic pesticidal agents lack solubility in plastic matrices such as thermoplastic or thermoset. Similarly, inorganic pesticidal agents are likewise insoluble in known thermoplastic or thermosetting polymers. Similarly, inorganic chemicals utilized as trace nutrients in agriculture are insoluble in plastic materials.
One method of causing an insoluble organic agent to emit from a plastic dispensing unit is to use a third phase material that is (1) soluble in some extent in said plastic, and (2) will carry said organic agent in solutions or serve as a migratory pathway for said agent to reach the surface of said dispenser. It is, of course, recognized that the incorporated agent must reach the plastic/external environment interface to have any effect on organisms inhibiting the external environment. U.S. Pat. Nos. 2,956,073 and 3,116,201 describe the use of plasticizers as carrier elements. In an improvement on such patents, U.S. Pat. Nos. 3,705,938 and 3,864,468 teach that surface loss from a plasticized matrix is subject to control through the use of a regulating membrane at said surface.
The controlled-release art has been generally confined to the incorporation and release of insecticides, bactericides, molluscicides and other toxic materials of an organic nature from an elastomer, wherein solubility is essential, or plasticized plastics, wherein an additive carrier material is critical. Microencapsulation processes, wherein an inner core of the toxic agent is surrounded by a polymeric matrix, is well known to the pest control art. In general, release is effected by the rupture of the enveloping membrane.
Little work has been hitherto performed in the development of efficacious long lasting fertilizing systems. U.S. Pat. No. 3,748,115 teaches that plant nutrients can be bound in a matrix of synthetic rubber, waxes, asphalt, and the like. In this work, four critical elements of the invention are set forth. The fertilizer, emphasizing bulk materials and not trace nutrients, must be uniformly dispersed in a hydrophobic binding element. The dispensing unit must be cylindrical in shape. Said cylinder must be partially coated with a water-insoluble, water-permeable exterior membrane. A portion of the cylinder must be non-coated with said membrane. U.S. Pat. No. 3,520,651 extends this art to reach that more than one nutrient can be incorporated in similar dispensing commodities.
Of course, fertilizing materials have long been compounded with various binders to facilitate dispersal and, in some cases, to prolong availability by slowing the rate of solution in water through precluding immediate nutrient element contact with water. U.S. Pat. No. 3,336,129 teaches that the use of small amounts of water insoluble copolymers and terpolymers of ethers, substituted ethers, ethylene oxide, and the like, will serve as carriers for fertilizing materials, said copolymers and terpolymers must be crosslinked. Materials are comprised of polymer+fertilizer+water+soil components and the plant is grown within this medium.
Also, fertilizers such as urea can be coated in a granular form as taught in U.S. Pat. No. 3,336,155, thus retarding solution in ground waters. U.S. Pat. No. 3,276,857 teaches that a fertilizer can be encapsulated with asphalt or various waxes and, thus, emission into the environment is slowed.
Other encapsulated patents include Japanese Pat. No. 4,428,457 wherein a granulated fertilizer leaches through a thin film; U.S. Pat. No. 3,059,379 wherein a fertilizer is encapsulated with the encapsulating film having holes or apertures therein; and U.S. Pat. No. 4,019,890 wherein granular fertilizers are coated with a water-resisting layer and forming a jelly-like gel coating thereon. U.S. Pat. No. 2,891,355 relates to coating shredded styrofoam with a solution of fertilizers and nutrients, adding water, and potting a plant therein. British Pat. No. 68,127 relates to utilizing very small amounts of a thermoplastic material as a binder to prevent bulk fertilizers such as urea, and other deliquescent nitrogen compounds from sticking together. Other patents in the area which do not relate to the present invention are Japanese Pat. No. 4,943,776 and U.S. Pat. Nos. 3,794,478; 2,791,496; 2,797,985; 3,372,019; and 4,111,684.
Turning to the area of larvicides, Boike et al. has shown in examining 23 different organotin formulations and solute elastomer formulations that they were not effective under practical use conditions due to the presence of natural or organic substances common to water courses. Said organic materials rapidly absorb organotin molecules, essentially removing them from mosquito larva contact. In a text by Cardarelli, 1976, it was taught that pesticides in an elastomer matrix can cause a slow-long duration release of the pesticide.
U.S. Pat. No. 4,012,347 relates to a rosin composition containing a film forming polymer, a solvent, and a pigment in which the rosin slowly flakes off, thereby exposing an organotin compound. U.S. Pat. No. 3,234,032 also relates to anti-fouling marine coating compositions wherein various organotin compounds are contained in waxes, oils, or paints. U.S. Pat. No. 3,236,739 relates to a bis(tributyltin)-adipate anti-fouling composition wherein the tin compound is dispersed in substantially water-insoluble film forming vehicles such as spar varnish, vinyl acetate-vinyl chloride copolymer paints, and the like.
In an article appearing in CHEMICAL ABSTRACTS, 75:97577c (1971), various non-organotin liquid pesticides are dispersed in various film-forming polymers, however, the system does not contain a porosigen or a water release system.
U.S. Pat. No. 4,010,141 relates to an organotin compound having a normal-dodecyl side chain such that the tin compound is soluble in and has bleedability from a thermoplastic. However, this patent fails to teach the use of a porosigen and actually teaches away from applicant's invention.